Two recent studies of “natural” health supplements have found that they often contain ingredients that can potentially be harmful and sometimes don’t even contain any of the ingredient they are represented as having.

In a column for USA Today, Dr. Kevin Pho saidÂ Americans spendÂ $5 billion a yearÂ on pills likeÂ echinacea,Â ginkgo bilobaÂ andÂ black cohoshÂ for various health ailments or to help improve their health. More thanÂ 29,000 herbal productsÂ are sold throughout North America, with aboutÂ half of AmericansÂ using some form of alternative medicine. He pointed out that many people believe these products to be safe because they are promoted as natural or organic, and legally sold.

However, a study by the journalÂ BMC Medicine, released last month, used DNA analysis to find that most of the 44 randomly selected herbal supplements they tested wereÂ “of poor quality, including considerable product substitution, contamination and use of fillers.”

One bottle of St. John’s wort, which is used to treat depression,Â contained pills that had no evidence of the advertised herb while another bottle of St. John’s wort the scientists studied had substituted another plant that is a known laxative.

The Food and Drug Administration recentlyÂ tested 21 “all-natural” dietary supplementsÂ and found that nine of them contained unlabeled amphetamine-like compounds, which, if taken in unmonitored doses, can lead to elevated blood pressure, rapid heart rate and heart attacks.

Last year, the FDA implicated the herbal industry in causing more thanÂ 50,000 adverse eventsÂ annually.

Some pills use fillers like black walnut, which can severely affect people with nut allergies. Others contain unlabeled toxic ingredients and many, like garlic and ginkgo biloba, also interact with prescription drugs, which can alterÂ the effectÂ of blood thinners and cause life-threatening bleeding.

Pho said that many people incorrectly believe that these herbal supplements are regulated by the FDA like prescription medications, which leads them to believe that they are safe, when, in fact, many are not.